Insights into the generation of hydroxyl radicals from H2O2 decomposition by the combination of Fe2+ and chloranilic acid

Abstract

In this work, the degradation of chloranilic acid (CAA) by chemical oxidation with H2O2 alone and in the presence of ferrous iron Fe2+ catalyst was investigated in order to improve our understanding on the novel metal-independent approach. The interesting and efficient metal-independent hydroxyl radicals (OH) production by using halogenated quinones and H2O2 has been currently demonstrated. The results clearly confirmed the formation of OH radicals from the reaction of CAA with H2O2. CAA was slowly decayed by chemical oxidation with H2O2 and followed a pseudo-first kinetics. H2O2 doses ≥ 1000 mM were required to achieve complete CAA decay from 1 mM CAA. However, low total organic carbon (TOC) removal was measured with the accumulation of carboxylic acids. The addition of Fe2+ enhanced the kinetics of CAA degradation and reduced the required dose of H2O2. High TOC removal was obtained, almost complete release of chloride ions, without accumulation of carboxylic acids. The decolorization of methylene blue (MB) aqueous solutions was performed using H2O2, H2O2/CAA, H2O2/Fe2+, and H2O2/CAA/Fe2+. H2O2/CAA/Fe2+ was the most effective method in decolorizing MB solutions due to the accelerated Fe2+ regeneration. Coupling Fenton reagent with CAA seems to be promising alternative to physical activation in water and soil treatment.